Fuel cell technology has been the subject of much recent research and development activity due to the environmental and long-term fuel supply concerns associated with fossil fuel burning engines and burners. Fuel cell technology generally promises a cleaner source of energy that is sufficiently compact and lightweight to enable use in vehicles. In addition, fuel cells may be located close to the point of energy use in stationary applications so as to greatly reduce the inefficiency associated with energy transmission over long distances.
Although many different fuels and materials may be used for fuel cells, all fuel cells generally have an anode and an opposing cathode separated by electrolyte. The anode and cathode are generally porous so that fuel may be introduced into the cell through one of them, generally the cathode, and oxidant introduced through the other, generally the anode. The fuel oxidizes in the cell, producing direct current electricity with water and heat as by-products. Each cell generally produces an electrical potential of about one volt, but any number of cells may be connected in series and separated by separator plates in order to produce a fuel cell stack providing any desired value of electrical potential. In modern fuel cell design, the anode, cathode, and electrolyte are often combined in a membrane electrode assembly, and the separator plates and current collectors are often combined in a “bipolar plate.” Details of fuel cell design and operation are further explained in “Fuel Cell Handbook, 5th Edition”, published by the U.S. Department of Energy, National Energy Technology Laboratory, Morgantown, West Va., October, 2000, hereby incorporated fully herein by reference. Various fuel cell components, including membrane electrode assemblies and bipolar plates, are further described in U.S. Pat. Nos. 4,988,583; 5,733,678; 5,798,188; 5,858,569; 6,071,635; 6,251,308; 6,436,568; and U.S. Published Patent Application Ser. No. 2002/0155333, each of which is hereby fully incorporated herein by reference.
A persistent challenge in the design of fuel cells is that of managing water in the cell. Under some conditions, water is evolved very quickly within the cell. This water is generally produced on the cathode side of the cell, and if allowed to accumulate, may restrict or block the flow of fuel into the cell. Such a condition is known in the art as “cathode flooding”. In addition, the temperature differences between the cell and ambient environment may be large so that condensation of water vapor may be caused at times as air moves in and out of the cell during operation.
Typically, the surface of bipolar plates is provided with drainage channels so that water is directed through the channels to a collection area to be drained from the cell. In addition, the bipolar plates are often made from material having relatively low surface energy so water drains from the bipolar plate more easily. Neither of these measures has been entirely successful in eliminating cathode flooding and water management problems in fuel cells, however. In particular, even where low surface energy materials such as PTFE are used in fuel cells, water droplets may cling to bi-polar plates and other surfaces in the cell rather than draining away as desired. What is needed in the industry is a fuel cell with components facilitating improved water drainage within the cell.